1. Field of the Invention
The present invention relates to an apparatus for producing seedlings and a method of producing seedlings, which make possible, in producing grafted seedlings of fruit vegetables, to perform a consistent process from the culture of their stocks (rootstocks and scions) to welding after grafting at low cost.
2. Description of the Related Art
For fruit vegetables of the nightshade family (including tomatoes and eggplants), cucurbits (including cucumbers and watermelons) and others, their seedlings produced by grafting a rootstock to a scion of each in order to add the characteristics of the rootstock (including pathological resistance) to the scion are extensively used as seedlings superior in productivity and pathological resistance to seedlings known as non-grafted seedlings which undergo no grafting.
These seedlings produced by grafting rootstocks and scions are called grafted seedlings. In a grafted seedling, the faces of a rootstock and a scion cut, either fully or partially, with a cutting tool are matched with each other and the matched faces are agglutinated while, in some cases, being supported with a clip or a tube. This agglutination, also called rooting, has an effect to connect the vascular bundle tissues of the rootstock and of the scion, and to transfer moisture and nutrients from the rootstock to the scion and the anabolic products of photosynthesis by the scion to the rootstock. Therefore, in attempting to improve the effective yield of grafted seedlings, it is essential to enhance the rooting rate of such grafted seedlings.
In order to facilitate this rooting of grafted seedlings, the conditions of the environment in which the grafted seedlings are placed after grafting are important and, in particular, the phase of environment control during the few days immediately after grafting is called welding. During the welding, the vascular bundles of the rootstocks and the scions should be connected to each other in their respective cut faces so as to establish communication routes for moisture, nutrients and anabolic products between the rootstocks and the scions. In such a high-temperature high-humidity environment of little exposure to sunlight, rooting is accelerated by restricting the evaporation of moisture through the stomata of the rootstocks and scions to thereby prevent the rootstocks and scions from drooping and restraining the drying of the area around the agglutinated faces. The welding of cucumbers, for instance, is often accomplished in an environment of high temperature, around 30° C., relative humidity of nearly 100% and a luminous intensity of 3000 to 5000 luxes when it is performed by a method known as young seedling grafting in which grafting is done immediately after the generation of true leaves of the rootstock.
In order to enhance the rooting rate of grafting by performing appropriate welding immediately after the grafting, conventional welding methods utilizing natural light in a welding facility (welding house or welding tunnel) have been extensively adopted. Namely, extensively applied methods using a welding facility include an artificially regulating method in which a tunnel covered with a covering material, such as a vinyl sheet, or a light-shield material is installed within a greenhouse, grafted seedlings are placed therein, and the air temperature and the relative humidity are adjusted by sprinkling water or opening or closing the tunnel covering material and the luminous environment is controlled with the light-shield material. On the other hand, another method using a welding apparatus is mainly used by seedling culture centers where grafted seedlings are produced year round, and has an advantage that, as the inside of the apparatus is a closed space isolated from the external environment, the environment therein can be automatically controlled as desired irrespective of climatic variations.
As a method of seedling culture using artificial light instead of natural light, there has been proposed a method utilizing a closed-type transplant production system as disclosed in, for instance Japanese Patent Laid-Open No. 2001-346450 (see FIG. 4 therein). This system is provided, in a closed space, with an artificial lighting unit using fluorescent lamps, multi-stage seedling culture shelves, an automatic irrigation unit, an air conditioning unit using an air conditioning for household use, a carbon dioxide gas supply unit and so forth, and environment control by the artificial lighting unit, the air conditioning unit and other devices makes seedling culture unaffected by the external climatic conditions possible.
However, these three methods involve the following disadvantages of their own.
First, the method using a welding facility requires fine artificial adjustment according to climatic variations in the ambience, resulting in a greater labor requirement for management. Moreover, welding under weak lighting tends to make the grafted seedling feeble and, since the seedlings themselves are apt to lack vigor and to catch illness due to slow progress of the photosynthesis, no significant growth after the fix planting can be expected. Furthermore, acclimatization by gradually increasing the luminous intensity is usually required after the welding and, as this acclimatization takes a week or longer, the seedling production process is extended correspondingly.
Next, by the method using a welding apparatus, as in the case of the above-described method using a welding facility, welding under weak lighting tends to make the grafted seedling feeble and, since the seedlings themselves are apt to lack vigor and to catch illness due to slow progress of the photosynthesis, no significant growth after the fix planting can be expected. Further, acclimatization by gradually increasing the luminous intensity is usually required after the welding and, as this acclimatization takes a week or longer, the seedling production process is extended correspondingly. Moreover, since the inner space requires a moisture-proof and waterproof structure (in this specification “water-proofness” is a broad concept covering moisture-proofness and drip-proofness as well) because of the environment control conditions, this not only is more expensive than a welding house but also the humid environment necessitates repairs. Namely, whereas fluorescent lamps are mainly used for the lighting unit, the fluorescent tubes are shielded by waterproof-structured covers, and the sockets of the fluorescent tubes are also totally closed. Also, the installation of a humidifier is indispensable, and mist from an ultrasonic humidifier and other sources is discharged into the inside of the apparatus. Whereas a humidity sensor has to be provided to control this humidifying operation, in a high relative humidity region of 95% or more, the detecting portion of the humidity sensor is usually susceptible to dew condensation, which means that deterioration of the detecting element is apt to progress. Furthermore, it is impossible to use an inexpensive household air conditioner for the temperature control purpose, but a refrigerating machine for business use, which is compatible with a high-humidity environment, is used. In this way, the welding apparatus has to be heavily equipped, requiring a waterproof structure and the like. As a result, it not only is more expensive than a welding house but also the humid environment necessitates repairs.
Finally, as the closed-type transplant production system using artificial light is an apparatus exclusively intended for seedling culture, and is embodied with no consideration for the subsequent welding, a separate welding apparatus has to be installed in addition, inviting an increase in the overall cost of the apparatus for producing seedlings.